Porous mold for the continuous casting of metals



I May 29, 1956 N. P. 6055 2,747,244

POROUS MOLD FOR THE CONTINUOUS CASTING OF METALS Filed July 15, 1953 2 Sheet-wSheet 1 .i. S. d J6 1: J5 B8 Q I l /2 I 14' my? /2\,

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Arrok/yzys' United States Patent POROUS MOLD FOR THE CONTINUOUS CASTING OF lVIETALS Norman P. Goss, Mayfield Heights, Ohio Application July 15, 1953, Serial No. 368,152

6 Claims. (Cl. 2257.2)

This invention relates generally to the art of metal founding and particularly to a new mold for the continuous casting of metals.

This application is a continuation-in-part of my copending application Serial No. 286,661 filed May 8, 1952, for Method and Porous Mold for the Continuous Casting of Metals.

Heretofore metals have been cast continuously by different methods. Various expedients have been employed by workers in the art to prevent the metal from frictionally engaging or adhering to the inner surfaces of such molds, often with resultant rupturing of the initially formed shell or skin of cooled metal followed by flow of still molten metal through the breaks in that shell.

This initially formed skin on the metal is very tender and the friction between this skin and the forming mold must be reduced practically to the point Where the cast bar will fall through the mold of its own weight. In other Words the pinch rolls usually regarded as pulling the cast bar through the mold are actually used in the case of my invention more to regulate the movement of the bar through the mold than to pull it through.

Previously known methods and apparatus for the continuous casting of metals, of which I am aware, failed to provide a substantially uninterrupted film of lubricant between the metal being cast and the mold wall over the entire area of contact at all times and continuously supplied to the interface between metal and mold in a film substantially continuously and uniformly spread over the entire interface as it reaches said interface.

The present invention aims to provide a mold which will be quite satisfactory in the continuous casting of metals, including both ferrous :and non-ferrous metals and particularly aluminum, and attains this object by providing a mold which may be lubricated automatically and substantially uniformly throughout a predetermined vertical portion of the inner surface of the mold.

riefiy described, this invention may be practiced by providing a mold wall or liner which is to engage with the metal being cast and which is sufficiently porous to permit liquid lubricant to pass therethrough slowly and uniformly, usually under some static head or pressure, and to cover substantially the entire inner surface of the mold over the portions thereof where danger of adherence of the molten metal to the mold might otherwise take place. This calls for lubrication over substantially the entire area of the mold contacted by the forming metal. Liners suitable for use in practicing this invention may be formed of several materials including porous or permeable graphite, with or without the initial inclusion of one or more substances capable of being volatilized under heat with the resultant creation of porosity or permeability in the finished article adequate for the present purpose.

An object of the present invention, therefore, is to provide a mold for the continuous casting of metals in which a film or lubricant is automatically maintained over substantially the entire inner surface of the mold which is ice in contact with the molten metal as its outer surface is changing into a solidifying shell. The invention includes the supply of lubricant through the mold Walls in very small discrete increments substantially evenly distributed over substantially the entire area of the mold contacted by the forming metal.

Another object of the present invention is to provide in a mold for the continuous casting of metal, a porous lining having particular properties so as to maintain a continuous film of lubricant or vapor between the newly formed skin on the metal and the walls of the casting chamber.

Another object of the present invention is to provide a mold in which heat is removed from the outer surface of the molten metal as the outer portion thereof is changing into a solidifying shell, and the inner surface of the mold and the outer surface of such shell are lubricated by a substantially continuous, automatically maintained and renewed film of lubricant.

A further object of the present invention is to provide in a continuous casting mold as above described means for controlling the supply of lubricant to the inner mold walls.

Still a further object of the present invention is to provide a mold as above described of a plurality of sections including provision for holding the sections axially aligned, means for preventing separation of the sections under variations in temperature, and other improve Fig. 3 is a central sectional view similar to Fig. 1 and showing a modification of my invention.

Apparatus suitable for carrying out my invention is shown in Figs. 1 and 2 of thedrawings. An inner cylindrical sleeve 10 of porous material is surrounded by an outer sleeve 11 of heat conducting material such as copper or aluminum and in heat conducting engagement with the sleeve 10. In a preferred form of my invention, I either provide a press fit of the sleeve 10 within the sleeve 11 or I heat the sleeve 11 and then shrink it on the sleeve 16. Preferably, some cooling means is provided for the sleeve 11, and in the present embodiment,

I have shown a Water jacket comprising the hollow chambers 12 in the sleeve 11 surrounded by a cover plate 13 and sealed against leakage at 14. Means, not shown, is provided for the circulation of a suitable cooling fluid through the chambers 12. Preferably, but not necessarily, I provide a plurality of casting sections in end to end relationship as shown in Fig. 1.

section have been given the same reference characters with a prime suflix.

Means is provided for holding each of the sectionsof the mold assembled and for holding the upper and lower sections aligned. This comprises a series of bolts 15 passingthrough a top collar or ring 16 of the upper mold section, a bottom collar 17 of the upper section, and a top collar 16' of the lower section. Each bolt 15 has a head 18 on one end and a nut 19 on the other end and these are drawn up rather tightly compressing very strong springs 20 held between the bolt head and nut and the rings 16 and 16 respectively. Another set of bolts 21 The parts having the same function in the lower section as those in the upperpasses through aligned openings in collar 17 and 16 and then through the bottom collar 17' of the lower mold section. These bolts have heads 22 and nuts 23 which are pulled up tightly against stilt springs 24 so as to hold the parts together fairly firmly but with a slight resiliency. The collars 16 and 17 hold the upper mold section together. The collars 16 and 17' hold the lower mold together, while the bolts and 21 passing through aligned openings in collars 17 and 16' hold the upper and lower mold sections in alignment. The springs and 24 permit the mold sections to expand under increasing temperature.

While additional mold sections might be provided, if desired, I prefer to utilize just sufficient travel through the mold sections previously described to form a solid skin onthe metal after which further cooling of the metal may be provided by a sleeve 25 of good heat conducting material, such as copper, depending below the lower mold section. This sleeve is provided with an annular shoul der 26 which is positioned inside the lower end of sleeve 11' and serves to hold the sleeve 25 aligned with the sleeve 10. A plurality of cap screws 27 are threaded into the sleeve 11 and press against lugs 28 which in turn engage beneath the annular shoulder 26 so as to hold the sleeve 25 in position. Preferably springs 29 are provided between the screw heads of the members 27 and the lugs 28 so as to hold the parts very firmly but slightly resiliently in place. Water sprays 30 are provided with a suitable source of water or other suitable coolant supply playing upon the outer face of sleeve 25 to keep the same cool so as to further cool the metal passing through the sleeve 25.

The sleeves 10 and 10 may be formed of several different materials. A preferred material is a graphite of known character having between 5 and 25 percent porosity as determined by filling the pores of the graphite with liquid lubricant whose volume is measured. A preferred form which I have used very successfullyhas approximately 17 to 20 percent porosity. It is almost impossible to buy graphite sufiiciently uniform and permeable for my invention by specifying porosity alone. I have had best success in casting aluminum while using graphite in which the particle size runs between approximately .005 and .032 inch. The pore sizes in these preferred graphites have ranged between approximately .002 and .018 inch. If the sleeve is too porous, frothing of the molten metal occurs within the graphite sleeve.

Such a graphite product is formed in a known manner by mixing finely divided graphite with a small proportion of tarry material, after which the mixture is molded under pressure and then subjected to heat so that the tarry material is burned away. I believe that as a result of this method of manufacture very fine openings are formed in the graphite structure, these openings being so small that they may be said to be capillary in character and interlaced and crisscrossed in a labyrinth of paths. It is important to the operation of my invention that there be no passages of substantial size and no direct path for the lubricant, about to be described, to flow too freely through the sleeves 10 and 10'. In a preferred form of my invention, the sleeves 10 and 10' are about one-quarter inch thick and their porosity or permeability is such that it takes an oil of good flowing properties (such as palm oil at room temperature) about ten minutes to Work through that one-quarter inch thickness under one hun dred pounds per square inch pressure.

Other suitable porous materials adapted for use inthe sleeves 10 and 10 are known as sintered metals compris-' the metallic ingredients to alloy with each other and to elfect the removal of the organic volatile substance so as to provide the desired porosity.

Other suitable compositions are taught in U. S. Patent No. 1,656,508 granted January 17, 1928, to Carl Claus; in U. S. Letters Patent No. 1,768,528 granted June 24, 1930, to Charles R. Short; and in U. S. Letters Patent No. 1,839,094 granted December 29, 1931, to Harvey D.

Geyer.

Other materials which may be formed into aggregates having suitable porosity for sleeve 10 or 10' are boron carbide, carborundum and beryllium oxide.

For feeding the lubricant to the upper section of the mold in Fig. l, I provide the lubricant in a reservoir 31 either under atmospheric pressure or under inert gas pressure sufiicient to cause the lubricant to pass through the porous sleeve 10. The lubricant is fed through the main feed line 32 to a manifold 33. Branch lines 34 then lead from the manifold through a boss in the sleeve 11 to the interface between sleeves 10 and 11. I have had satisfactory results with no further structure than this because I find that the oil passes over the entire interface between the sleeves 10 and 11 and then works its way through the sleeve 10 to the interface thereof in contact with the forming metal. However, in order to assure good distribution of the oil, I provide a shallow groove about inch deep as indicated at 35 entirely around the sleeve 10. I may then provide vertical grooves 36 of about the same depth communicating with the groove 35 and extending upwardly and downwardly on the outer face of the sleeve 10 in axial direction. If the normal level of molten metal in the casting chamber is at the dot-dash line A as indicatedin Fig. 1, then I prefer to terminate the vertical grooves 36 short of that level. I find it is desirable to feed only very slight amounts of oil to the inner face of the sleeve 10 at the zone .where the molten metal first engages the interior surface of the sleeve. Too great a flow of oil at this point will cause foaming of the molten metal when casting aluminum. However, if the grooves 36 are terminated somewhat below the level of the line A in Fig. 1, the oil will work through the capillaries of the sleeve 10 to its interior face for an inch or two above the tops of the grooves 36. I prefer a microscopic film of oil near the metal line when casting aluminum, but may use more lubricant at a lower level.

Suitable oils for use as lubricant in my invention for feeding through the reservoir 31 and conduits 32, 33 and 34 are a machine oil of approximately SAE 20 viscosity, or paraffin oil, or palm oil. Of these, I prefer palm oil. Any of these oils may be mixed with colloidal graphite, 5 to 10 percent by volume, and will still pass through por ous sleeve 10 if the sleeve 10 is of greater porosity, and assuming that the sleeve 10 may be replaced if its pores become clogged. In any case, the oil should be such that under the temperature conditions occurring in the sleeve 10, the oil will flow slowly through the sleeve 10, so as to deposit no more than a thin film of oil on the inner surface of sleeve 10.

I have noted that when the sleeve 10 is made of graphite of approximately 17 to 20 percent porosity and when no metal is in the mold, the lubricant palm oil, under lbs. per square inch pressure, and at approximately 70 degrees Fahrenheit, works through the sleeve 10, one quarter inchthick, as a fine, almost microscopic, sweat showing little beads not over 1/ inch apart on the inner face of sleeve 10 and almost invisible to the eye. When the mold is'in use, these beads coalesce or diifuse and form a thin film of substantially uniform thickness and covering substantially all the area ofthe inner surface of the sleeve over which'a lubricating effect is desired. This film is maintained by constant or intermittent addition of oil from the reservoirto'compensate for the oil which is volatilize'd or carried away by the metal being cast.

. In the use of the mold as shown in Figs. 1 and 2, the

wall area contacted by the forming metal.

porous sleeve 10, and preferably also, are first charged with lubricant oil under pressure until they are completely charged with oil. The apparatus is then assembled as shown in Fig. l and lubricating oil is supplied from reservoir 31 and the connected conduits. The molten metal vides just the necessary amount of lubricant so that the metal is substantially friction free as it passes through the mold. There is a substantially continuous oil path from reservoir 31 through conduits 32, 33, 34, 35 and 36, and through sleeve 10, to replenish the oil film on the inner face of sleeve 10 as fast as it is used up in the casting process. Some of the oil on the inner face of sleeve 10 is immediately vaporized by the heat of the metal and passes upwardly between the metal and the inner face of sleeve 10, burning at the top. This filling of the air gap between the metal and the mold wall with an oil K vapor prevents access of air to the surface of the metal as it passes through the mold and therefore, I obtain a very bright unoxidized surface.

The cooling sleeve 11 is in heat-conducting relationship with the sleeve 10 over substantially the entire mold Any slight gap between sleeves 10 and 11 is filled with heat-conducting lubricant.

I find that no matter how carefully the parts are fitted, a certain amount of oil will travel downwardly along the faces 38 and 39, emerging at the inner face of the mold passageway between the sleeves 10 and 10. This additional oil is sufficiently below the normal metal level at A that it does no harm and facilitates the further movement of the hardening metal through the sleeve 10.

It will be noted that the porous sleeve 10 within the outer sleeve 11 overlaps the end of the sleeve and enters into the metal sleeve 11'. This aids in keeping the upper and lower sections of the mold properly aligned.

It will be noted that a slight shoulder has been indicated at 40 where sleeves 10 and 10 meet; and another slight shoulder at 41 where the sleeves 10' and 25 meet. This is in accord with the teaching of my Patent No. 2,527,545 granted October 31, 1950, and is very useful in connection with the present invention. However, the present invention will operate with or without the shoulders 40 and 41.

To provide a control of the oil filling the gaps between the sleeves 10 and 11, I provide a plurality of vents 42', as shown in Fig. 2, extending from the groove 35 outwardly through the sleeve 11 to atmosphere. Preferably, I provide valves 65 on these vent lines so that the air may first escape when the sleeve 10 is being completely charged with oil and so that the valves 65 may be closed whenever necessary to build up pressure sufficient between sleeves 10 and 11 to cause the lubricant to pass through the sleeve 10 in the quantities desired.

In the modification of Fig. 3, the construction is for the most part similar to that already described. In the upper mold section the porous sleeve 42 surrounded by the metal sleeve 43 is like the sleeve 10 and outer sleeve 11 of Fig. 1. Where necessary or desirable to build up greater pressure to force the oil through the sleeve 10 I provide valve means for closing vents 42' after the excess air is expelled from the oil system. Water jackets 44 are provided to cool the outer sleeve 43. In the lower mold section the inner sleeve 45 and the outer sleeve 46 are similar to sleeves 10' and 11' of Fig. 1 except the sleeve 45 is provided for lubrication in a manner similar to sleeves 10 and 42. Other cooling jackets 47 are provided for the lower mold section. Annular collars 48, 49, 50 and 51 are held together by sets of bolts 52'and 53 exactly as provided in Fig. l. The sleeve 25 is similar in all respects to sleeve 25 of Fig. 1 and is held on in a similar manner by bolts 54 and is cooled by coolant sprays, not shown.

There are two fundamental diiferences between Fig. 3 and Fig. l. The first difference is that from reservoir 31a the lubricantis fed through lines 32a and 55 to the upper mold section, while from reservoir 31b (at a level higher than 31:!) the lubricant is fed through lines 32b and 56 to the lower mold section. Each of these lines 55 and 56 connects with a manifold like 33 in Fig. 2 and supplies lubricant at spaced points about the generally cylindrical sleeves 42 and 43. Other vent lines are provided at 57 similar to the vents 42 of Fig. 2. These vent lines 57 may have valves like 65, if desired. Valves 55a and 56a are provided in lines 55 and 56 respectively so as to control the flow of lubricant to the upper and lower mold sections. In one form of my invention, I close the valve 55:; so that only a small amount or no oil is fed to the upper mold section, instead, the oil being fed through line 56 to the lower sleeve 45 and the vapor passes upwardly between the forming metal and sleeve 42 so as to provide lubricant to the degree needed in the upper mold section. Furthermore, if desired, the valve 55a may be opened intermittently to allow additional lubricant to fill the annular groove 35' and the vertically branching grooves 36'. with a small amount of lubricant as needed. Or valve 55a may be open and valve 56a may be closed to provide lubricant similarly to Fig. 1. When both valves 55a and 56a are open, lubricant flows to the lower section under greater head than to the upper section. With sleeves 42 and 45 of similar porosity, this provides more oil in the lower section where the metal skin is thicker. Thus, Fig. 3 provides for the feed of lubricant to the porous sleeves 42 and 45 in both the upper and lower mold sections, or in either one separately. This same arrangement of lubricant feed could be provided in Fig. l in connection with the sleeve 10 if desired.

Another difference between Fig. 3 and Fig. l is in the arrangement whereby the sleeves 42 and 45 are prevented from parting at the level 58 under certain temperature conditions. To prevent this, the interface between sleeve 42 and sleeve 43 is slightly frusto-conical in form with the greater diameter at the zone 59 and the smaller diameter at the zone 60. In a similar manner the sleeve 45 is frusto-conical with its greatest diameter at 61 and its lesser diameter at 62. When the mold is assembled, as shown in Fig. 3, there is a slight gap of the order of 20 or 30 thousandths of an inch at 63 between the collars 49 and 50. The sleeves 43 and 46 therefore are pulled toward each other and exert a pull on the porous sleeves 45 and 42 toward the zone 58. As the sleeves 42 and 45 increase in temperature they are held tightly together at the zone 58 and no objectionable air gap occurs there. The taper on the side walls of the outer faces of sleeves 42 and 45 are preferably of the order of about 30 to 40 thousands of an inch per foot of length. It is understood that the innerfaces of sleeves 42 and 45 are substantially cylindrical. The sleeves 42 and 45 are made of the materials found suitable for the sleeve 10 and previously described.

I may also provide a slight groove 64 in sleeve 45 heading downwardly from groove 36' and extending to, or near, the zone where sleeves 45 and 25 join. This may be done to insure a flow of lubricant down the inside of sleeve 25'.

In both the forms shown in Fig. l and Fig. 3, the mold sections are preferably ten to fifteen inches long in a vertical direction in a preferred form of my mold for casting bars of aluminum one to two inches in diameter and the sleeve 25 or 25 is twenty-four to thirty-six inches long.

It will be noted in both forms of my invention, that there is a continuous oil path from the outside feeding conduit to the inner face of the porous sleeve. All interstices are continuously kept filled with oil as the oil seems to be drawn out at the inner face of the porous sleeve by the action of the heat or by the wiping away of the oil film by the metal. The lubricant filled graphite sleeve and the lubricant film between the sleeves 10 and 11 in Fig. l, or sleeves 42 and 45 with their surrounding sleeves in Fig. 3, gives a good heat conducting path from the hot metal on the inside to the water jacket on the outside.

The porous graphite preferred for sleeve 10, has good dimensional stability, whereas dense graphite under percent porosity will warp under heat.

Hereinabove I have described by my invention using oil as a lubricant. I also contemplate that my invention might be used with lubricants of an oily character thick enough to be called greases. Any grease would be satisfactory for my purposes, if, upon being subjected to the heat of the casting opertaion, it became sufficiently fluid to pass through the porous sleeve 10, 42, or 45. In the use of such a grease, it is heated to a liquid state and then forced under pressure through one of these porous sleeves which I have described (disassembled from the mold) until the entire sleeve is charged with the lubricant. Then, upon cooling, the sleeve is completely charged with lubricant. In use, such a charged sleeve, in position in the mold, will slowly give up its lubricant during the casting process and may be used for a long period of time,

.after which, the sleeve would either be thrown away or it might be recharged and used over again.

In casting metals of higher melting point, such as steel, by the use of my invention, certain oil lubricants cannot be used because they will burn or vaporize too rapidly. In such a case, I may utilize a hydrocarbon gas which breaks down and deposits finely divided carbon when subjected to heat. One such gas is acetylene. In this form of my invention, the reservoir 31 of Fig. 1 is a closed container filled with acetylene gas under pressure. This gas is fed from the container 31 through lines 32, 33 and 34 to the face between sleeve 10 and sleeve 11. The gas, such as acetylene, would then pass through the sleeve 10 to the inner face thereof. After issuing from the microscopic pores in the inner face of sleeve 10, the acetylene gas breaks down upon contact with the hot metal being cast. The acetylene then deposits finely divided carbon over the entire inner face of the sleeve 10 so as to lubricate the passage of the metal through the mold. Where, in the claims, I have called for means for introducing, to the interior of the mold, through the porous sleeve, material providing lubrication for the passage of metal through the sleeve, I intend to include hydrocarbon gases such as acetylene which break down inside of sleeve 10 under heat to provide finely divided carbon lubricating the passage of the metal through the mold.

It will now be apparent that my invention provides lubrication for a mold, in which metal is continuously cast, so arranged that it is practically impossible for the metal to touch an unlubricated spot on the mold surface in contact with the metal. This is true because the lubricant passages opening through the inner surface of the mold wall are so close together that lubricant passing through them will have to spread hardly at all in order to provide a continuous lubricant film over the entire surface of the mold in the predetermined metal-skinforming area, and my invention will maintain and renew a substantially continuous film of lubricant over that area of the inner wall of the porous mold part.

Certain of the prior art known to me, and now used for the continuous casting of metals, i limited as to the speed of the metal passing through the apparatus because none of these molds, known to me, reduces the friction between the mold and the metal being cast to such a great extent as I am able to do with my improved invention described herewith. Because the friction is substantial in these prior molds known to me, the movement of the metal through the mold must be held to a slow speed. My invention, as taught herein, reduces the friction to such a very low point that I may make my mold much longer than the prior art molds quite commonly limited to nine inches. The use of the longer mold permits the metal to be moved faster through the mold while still giving it a long enough period in the mold to have formed a strong skin when the metal issues from the mold. My invention reduces the friction between the metal and the mold to such a low point that in actual practice an aluminum bar one inch in diameter, when cast in a porous sleeve mold of the type herein described, eight inches long, fell through the mold by its own weight, there being insufficient friction to hold the bar in the mold.

One of the difficulties in the continuous casting of metals has to do with the low melting point eutectics which are the last portions of the metal to freeze and which have a tendency to stick to the mold walls. My improved mold prevents this. One of the most difficult metals to cast continuously is aluminum. It may contain eutectics which remain liquid near 900 degrees Fahrenheit. My invention successfully casts aluminum and its alloys. I have mentioned previously the bad effect of too much oil at the metal line, or the top level of the molten metal in the mold. More than a microscopic film of oil on the mold wall causes foaming of aluminum at this zone. Since some of the low melting point eutectics of aluminum remain liquid for a little distance down the side of the mold wall, during metal travel, my mold may be used successfully in this connection as the sleeve 10 in Fig. 1 may be long enough to insure a minimum of lubricant on the internal wall of sleeve 10 until these low melting point eutectics have sufficiently solidified so that they do not react with the lubricant.

Aluminum, when cast in the open air, forms an oxide which floats and finds its way into the air gap between the metal and the mold wall. With my process, this oxide does not stick to the mold wall but instead adheres to the surface of the bar going through the mold and does not scratch the mold or scratch the bar in any way.

A typical casting of aluminum was poured through equipment similar to that shown in Figs. 1 and 2 using the following practice. The metal utilized was 14-8 aluminum wrought alloy, with a nominal composition of 4.4 percent copper, 0.8 percent manganese, 0.4 percent magnesium, 0.8 percent silicon, and the balance aluminum. This aluminum alloy was poured from a temperature of approximately 1210 degrees Fahrenheit into the upper end of the sleeve 10 of Fig. I wherein the internal diameter of the sleeve 10 was approximately 2% inches in diameter. The pinch rolls were operated at a speed to permit this aluminum bar to emerge from the mold at approximately 3 /2 feet per minute and the cast aluminum bar was of high quality metal with a very smooth external surface.

During the above casting, a narrow brown ring of oil was observed at the metal line where the metal engaged the mold wall. This is an indicator that the oil is feeding through the porous sleeve at the proper rate. If more than a narrow ring to A; inch) appears, frothing of the oil in the metal is likely to occur. If less than this appears, it may indicate too little lubricant with danger of the metal sticking to the mold wall.

Wherever in the specification or claims I have used the expression labyrinth of fine pores I mean to include materials which contain tremendously constricted and almost infinitely interlaced paths by which a fluid passes from the outer wall of my porous sleeve to the inner wall thereof.

Since it is impossible to give dimensions as to the fine pores in the porous sleeve 10, or other porous sleeves described above, I can onlyadd that in the porous graphite I have described above, the pores are invisible to the unaided eye. Also, from observing the action of this porous sleeve, it is my opinion that it act like a wick, so that, if the sleeve is in contact with liquid oil at any point, the wick action will carry the oil to all parts of the sleeve.

Wherever in the claims I have referred to uniform porous material in the lubricating sleeve, I mean that the material is as uniform as is commercially possible.

What I claim is:

1. A mold for the continuous casting of metal from the molten state comprising a cooled tubular sleeve of heat conducting material, a sleeve of porous material of high heat conductivity having a labyrinth of fine interconnected capillary pores and disposed inside of said first named sleeve, said porous sleeve being in heatconducting contact with said first named sleeve over substantially the entire area of the outer face of said porous sleeve save for lubricant supply passages, and means for introducing in said passages a lubricant adapted to pass through said pores.

2. The combination of claim 1 wherein said lubricant supply passages comprise a plurality of shallow grooves in the outer face of said sleeve of porous material, said grooves extending generally lengthwise of said sleeve and terminating short of the end thereof where molten metal is introduced.

3. The combination of claim 1 wherein said sleeve of porous material is graphite.

4. A mold for the continuous casting of metal from the molten state comprising two of the sleeves of porous material disposed respectively inside of two of the cooled tubular sleeves as defined in claim 1 in vertical end-toend relationship and having their inner surfaces in concentric register, and the zone of end-to-end engagement between said two cooled tubular sleeves being at a different level from the zone of engagement between said porous sleeves.

References Cited in the file of this patent UNITED STATES PATENTS 2,131,070 Poland Sept. 27, 1938 2,225,373 Goss Dec. 17, 1940 2,376,518 Spence May 22, 1945 2,618,032 Traenkner Nov. 18, 1952 FOREIGN PATENTS 742,771 Germany Dec. 10, 1943 837,589 Germany Apr. 28, 1952 OTHER REFERENCES PB 1 83,513 German patent applications on foundry work (FIAT Microfilm Reel D 39) Frames 1947 to 1951, inclusive, 1952A and 1952B. Offered for sale on page 1016 of Bibliography of Scientific and Industrial Reports, Oflice of Technical Services, U. S. Department of Commerce, vol. 9, No. 11, June 11, 1948. 

1. A MOLD FOR THE CONTINUOUS CASTING OF METAL FROM THE MOLTEN STATE COMPRISING A COOLED TUBULAR SLEEVE OF HEAT CONDUCTING MATERIAL, A SLEEVE OF POROUS MATERIAL OF HIGH HEAD CONDUCTIVITY HAVING A LABYRINTH OF FINE INTERCONNECTED CAPILLARY PORES AND DISPOSED INSIDE OF SAID FIRST NAMED SLEEVE, SAID POROUS SLEEVE BEING IN HEATCONDUCTING CONTACT WITH SAID FIRST NAMED SLEEVE OVER SUB- 